Iridium(III) complexes bearing oxadiazol-substituted amide ligands: color tuning and application in highly efficient phosphorescent organic light-emitting diodes

By adjusting the conjugation degrees of the phenylquinoline-based cyclometalated ligands, yellow, orange to red phosphorescent iridium(III) complexes [Ir(bzq)2(POXD)] (1, bzq = 7,8-benzoquinoline, POXD = N-(5-phenyl-1,3,4-oxadiazol-2-yl)-diphenylphosphinic amide), [Ir(pq)2(POXD)] (2, pq = 2-phenylquinoline) and [Ir(piq)2(POXD)] (3, piq = 1-phenylisoquinoline) have been designed and prepared. Their photophysical and electrochemical studies and theoretical calculations were performed, and [Ir(bzq)2(POXD)] was also determined by X-ray crystallography. At room temperature, complexes 1–3 exhibit efficient phosphorescence emissions at about 539, 592 and 614 nm with photoluminescence quantum yields (PLQYs) of 0.21, 0.06 and 0.06 in CH3CN solutions, respectively. In the 5 wt% doped poly(methyl methacrylate) (PMMA) film, the PLQYs (0.35 for complex 1, 0.37 for complex 2 and 0.18 for complex 3, respectively) increase significantly. Organic light emitting diodes (OLEDs) based on these complexes were fabricated to evaluate their potential application. The yellow device in the configuration ITO/2-TNATA (25 nm)/NPB (5 nm)/TCTA (10 nm)/complex 1 (10 wt%):mCP (10 nm)/complex 1 (10 wt%):TPBi (10 nm)/TPBi (40 nm)/Liq (1 nm)/Al (100 nm) shows excellent performance with a maximum luminance of 24 080 cd m−2, maximum current efficiencies of 70.1 cd A−1 and maximum external quantum efficiencies of 21.3% along with low efficiency roll-off.